The present invention relates to a piston-cylinder assembly. The invention is particularly useful in Stirling cycle machines, and is therefore described below with respect to this application, but it will be appreciated that the invention could advantageously be used in other applications including piston-cylinder assemblies.
One type of piston-cylinder assembly, commonly used in a Stirling cycle machine, comprises a cylinder, a piston head movable within the cylinder, a drive for effecting relative reciprocatory movements between the piston and cylinder, and a rolling or bellows diaphragm connected between the cylinder and the piston to define an expansible-contractible chamber containing a working gas. The rolling or bellows diaphragm thus forms a dynamic seal preventing the penetration of oil or gas into the expansible-contractible working chamber. However, a disadvantage in this type of construction is that the diaphragm is subjected to a large pressure difference on its opposite faces, which places a tremendous stress on the diaphragm and greatly shortens its useful life. Another disadvantage in such a construction is that the diaphragm produces a relatively large "dead volume" in the working chamber, thereby substantially decreasing assembly.